AM3 Socket and DDR3 Memory SupportThe new Phenom II X4 955 and 945 processors can still make good use of the AM2+ socket, the very same socket used by existing Phenom X4 and X3 processors, as well as Athlon-based processors. Although the introduction of DDR3 memory support is new on this launch, the on-die controller is able to use either DDR2 or DDR3 memory.
Motherboard makers have already released BIOS updates enabling their current AM2+ motherboards to support the Phenom II X4 940/920 processors. There is now a new wave of updates adding support for the Phenom II X4 955/945 processors on these older motherboards.
We like to believe this is the perfect upgrade path, as those who invested in a Phenom platform a year ago need only to purchase a newer more powerful processor to get a boost. This also allows those looking to build a new Phenom-based PC to choose from a huge range of mature AM2+ motherboards. The groundbreaking 790GX chipset also supports the Phenom II X4, offering enhanced tuning via its advanced clock calibration feature.
Keep in mind however that although the Phenom II X4 955/945 processors will work on AM2+ motherboards, older processors will not work on the AM3 platform. The AM3 socket has two less pins (938), making it mechanically incompatible with older 940-pin AM2/2+ processors. Besides the pin compatibility issue, the real problem lies within the on-die memory controller of these older processors, which does not support DDR3 memory.
Unlike the LGA1336 (Core i7) socket, the AM3 socket is capable of running either DDR2 or DDR3 memory, but not both on the same motherboard. At least today that sounds like an excellent option to have, given DDR3's pricing compared to DDR2. Like previous AMD processors the Phenom II X4 955/945 processors feature a dual-channel memory controller. The maximum officially supported DDR2 frequency is 1066MHz while DDR3-1333 is also supported.